The present invention relates to hypodermic syringes having a retractable needle to prevent accidental puncture of patients or medical personnel after use of the syringe. More particularly, the invention provides a fail safe structure for withdrawing the needle into the barrel of the syringe after use in such a way as to prevent subsequent access to the needle except by destruction of the barrel.
The existence of a number of highly infectious viral diseases to which medical personnel in hospitals and clinics are exposed has prompted the development of a number of different types of safety features in medical devices and particularly in hypodermic syringes. The reason for this is that accidental puncture with the needle in the use of a syringes is a frequent cause for transmission of infection and one that can be avoided by proper and careful handling steps that are required. However, such steps often take additional time which medical personnel do not have especially when functioning under emergency circumstances.
To accommodate the frequent emergency situations in which hypodermic syringes are used, the prior art has developed a number of different structures for preventing post use accidents. Several of these techniques have employed shields which are placed over the used needle typically in a non-removable manner. These solutions suffer from the disadvantage that the user must carefully insert the shield while avoiding the puncture and this typically results in additional loss of time. Other techniques employ the retraction principal where the user pulls the needle back into the barrel. While this is useful in terms of safety and requires less time, the prior art structures have been generally impractical to manufacture at low expense and some have not safely maintained the needle in a non-accessible position.
Present manufacturing techniques for mass producing hypodermic syringes of the disposable type must meet a number of strict manufacturing standards to qualify for medical use. Further, the manufacturing steps required should be the minimum necessary to qualify for medical use and still be consistent with the disposable character of the article. Also, it is highly desirable that the retracted needle be inaccessible except through destruction of the barrel to lessen or eliminate subsequent improper use of the syringe.
A number of the hypodermic syringe structures proposed in the prior art unfortunately require unduly complicated manufacturing techniques which materially increase the cost of the syringes. Other procedures require a complete redesign of the existing manufacturing lines and thus discourage their widespread implementation.
The present invention provides an effective retraction structure for hypodermic syringes that positively blocks access to the used needle once retraction has been effected. Moreover, the structure of the present invention will not materially increase the cost of the disposable type syringes while affording added protection to medical workers and patients working in connection with infectious diseases. Additionally, the structure of the hypodermic syringe of the present invention can be easily manufactured with a modest restructure of existing manufacturing facilities.
In a preferred form, the present invention utilizes a needle carrying hub where the needle extends beyond the rear face of the hub a limited distance and which is retained in the hub outlet channel by an easily frangible adhesive. When the plunger of the syringe is pushed into the barrel to discharge the contents of the barrel, a locking member mounted on the forward end of the plunger engages the projecting end of the needle and holds the end of the needle to allow the user to retract the needle by retracting the plunger which action breaks the frangible adhesive. At a point along the barrel, a detent is located which engages a portion of the locking member as the plunger with the needle is retracted. The detent prevents further movement of the locking member and effects breakage of the connection between the plunger end and the locking member thus preventing issuance of the retracted needle by the plunger.